I'd like to share some tips with you lovely people as this is the second time I bagged this achievement and there's a few things to note along with the above solutions.
1. Have more than 8 people on your friend list that are boosting this. It's a necessity simply for the fact that you will need to work on this achievement constantly for a few hours a day for 10 or so days running. Having a mix-match squad online at most times will account for missing players on different continents, and its great to have a team ready to go quickly. This is actually not as hard as it sounds as approximately 3% of people you run into play this game legit, and most you run into will be down with boosting. Just simply send a message saying "Flag Boost" in the lobby, and they will let let you know.
2. Check your NAT. If your NAT ain't open, correct it. This can affect if players can join each other in the CTF lobby, and it can extend the time you need to search for a game dramatically.
3. Keep it 10 player minimum a game. The reason for this is that if there are more than 4 people around the flag, someone will lose out on points.
4. Start up other peoples games if they are not boosting, then quit. As stated in the above solutions, the host is the second person down, and if your sure the guy is an anti-booster, start up his game, quit, then search again, and you should be anti-booster free.
5. Take note of who isn't an anti-booster immediately and try to convert them / give them the "Treatment". The "Treatment", is where one person kills him, and someone else revives him, constantly. People will eventually get annoyed and leave.
6. Punish those anti-boosters. There are some seriously sad, sad people that roam the lobbies of Call of Duty 3 looking to ruin your boosting sessions. These people are Bonafide Jerks, and they generally have a bio that clearly states "Modern Warfare is a load of crap, CoD 3 forever!!". You have every right to file a complaint against them and (hopefully) get them banned for a day or two, because if you have 9 people boosting, and 1 guy running around messing it up, then that's 1 guy affecting 9 other peoples game. Get him banned, people! Don't feel hard on yourself, about 4 people play this game legit anymore, and I think it's so ungrateful these guys hang around on here instead of playing the newer games that get made for us.
7. When the host is creating lag, don't over do it. Have a few windows open, or if you have Fiber-Optic broadband, upload a torrent. You don't want to lag out the game.
8. Install the game to your HDD. The game has a tendency to freeze up mid-game and mid-lobby so ripping it to the hard drive will reduce the risk of this happening.
9. If your friends snag General before you, have them hang around as "ABP", the Anti-Boosting Police. Responsibilities include monitoring checkpoints when a randomer is running around the map, Giving the treatment, Flag throwing if needed, and just generally to keep the peace. There's nothing more intimidating for an anti-booster than to be set upon by your cohorts, as there ain't much he can really do that will affect them.
10. *Don't be Racist*. It might seem like a good idea to massacre that one French kid on your team repeatedly, or to run over the Czech guy in a tank just because he wont understand when you say "Flag Boost", but hold on first. This achievement is sought after by Boosters from all over the globe, give them a second to show you their intentions, or let them catch on to what your doing.
11. If you happen to have the easy job of sitting round the flag collecting those juicy points, Show some courtesy. DO NOT CONSTANTLY MOVE AROUND. Your position and stance have absolutely NO Bearing on the points you will acquire, that's all down to your connection to the host. Ideally, you should stand in a C shape in front of the flag thrower, and crouch just in case the thrower lets of a shot by accident.
12. If your the flag thrower, then you need to perfect your skill to maximize your points per game. Look for the "Sweet Spot". There is a spot by the flag in which you don't have to move back and forth to grab it, you can simply hold the Right Trigger and tap the X button to grab it. Also, swap to your pistol, you can throw the flag much faster as opposed to having your shotgun out.
I hope these tips will be helpful along the road to achieving General and the other rank-based achievements. Good Luck Guys!